The global energy crisis has caused increased interest in alternative approaches to production of fuels. Biofuels for transportation are attractive replacements for gasoline and are rapidly penetrating fuel markets as low concentration blends. Biomass derived biofuel production has emerged as a major approach in increasing alternative energy production and reducing greenhouse gas emissions. The production of biofuels from biomass enables energy independence has been shown to enhance development of rural areas and enhance sustainable economic development.
First generation liquid biofuels utilise carbohydrate feedstocks such as starch, cane sugar, corn, rapeseed, soybean, palm and vegetable oils. The first generation feedstocks present a number of significant challenges. The cost of these carbohydrate feed stocks is influenced by their value as human food or animal feed, while the cultivation of starch or sucrose-producing crops for ethanol production is not economically sustainable in all geographies. The sustained use of these feedstocks as a source for biofuels would inevitably place great strain on arable land and water resources. Therefore, it is of interest to develop technologies to convert lower cost and/or more abundant carbon resources into fuels.
Second generation biofuels are those produced from cellulose and algae. Algae were selected to produce lipids due to their rapid growth rates and the ability of algae to consume carbon dioxide and produce oxygen.
One area that has seen increased activity is the microbial synthesis of lipids which comprise the raw materials required for bio fuel production. Numerous studies have demonstrated an ability to accumulate lipids through the use of oleaginous yeasts on different substrates such as industrial glycerol, acetic acid, sewage sludge, whey permeate, sugar cane molasses and rice straw hydrolysate. Again these second generation biofuel technologies have encountered problems due to high production costs, and costs associated with the transport and storage of the feedstock.
It has long been recognised that catalytic processes may be used to convert gases consisting of CO, CO2, or hydrogen (H2) into a variety of fuels and chemicals. However, microorganisms may also be used to convert these gases into fuels and chemicals. These biological processes, although generally slower than thermochemical processes, have several advantages over catalytic processes, including higher specificity, higher yields, lower energy costs and greater resistance to poisoning.
The production of acetic acid, acetate and other products such as ethanol by the anaerobic fermentation of carbon monoxide, and/or hydrogen and carbon dioxide has been demonstrated. See, e.g., Balch et al, (1977) International Journal of Systemic Bacteriology., 27:355-361; Vega et al, (1989) Biotech. Bioeng., 34:785-793; Klasson et al (1990) Appl. Biochem. Biotech., 24/25: 1; among others.
Acetogenic bacteria, such as those from the genus Acetobacterium, Moorella, Clostridium, Ruminococcus, Acetobacterium, Eubacterium, Butyribacterium, Oxobacter, Methanosarcina, Methanosarcina, and Desulfotomaculum have been demonstrated to utilize substrates comprising H2, CO2 and/or CO and convert these gaseous substrates into acetic acid, ethanol and other fermentation products by the Wood-Ljungdahl pathway with acetyl co-A synthase being the key enzyme. For example, various strains of Clostridium ljungdahlii that produce acetate and ethanol from gases are described in WO 00/68407, EP 117309, U.S. Pat. Nos. 5,173,429, 5,593,886, and 6,368,819, WO 98/00558 and WO 02/08438. The bacterium Clostridium autoethanogenum sp is also known to produce acetate and ethanol from gases (Aribini et al, Archives of Microbiology 161, pp 345-351 (1994)).
Acetobacterium woodii, a strictly anaerobic, non-spore forming microorganism that grows well at temperatures of about 30° C., has been shown to produce acetate from H2 and Co2. Balch et al. first disclosed the bacterium A. woodii which grows by the anaerobic oxidation of hydrogen and reduction of carbon dioxide. Buschorn et al showed the production and utilisation of ethanol by A. woodii on glucose. Fermentation of A. woodii was performed at glucose (fructose) concentrations of up to 20 mM. Buschorn et al found that when the glucose concentration was increased to 40 mM, almost half of the substrate remained when A. woodii entered the stationary growth phase, and ethanol appeared as an additional fermentation product. Balch et al found that the only major product detected by the fermentation of H2 and CO2 by A. woodii was acetate according to the following stoichiometry; 4H2+2CO2→CH3COOH+H2O.
Acetate can be an undesirable fermentation product, as it is challenging product to recover from an aqueous fermentation broth and has limited commercial use.
It is an object of the present invention to provide a process and fermentation system that goes at least some way towards overcoming the above disadvantages, or at least to provide the public with a useful choice.